The superior oblique muscle originates from the orbital apex, above the annulus of Zinn, and passes anteriorly and upward along the superomedial wall of the orbit. The muscle becomes tendinous before passing through the trochlea, a cartilaginous saddle attached to the frontal bone in the superior nasal orbit. The combination of the trochlea and the superior oblique tendon is known as the tendon–trochlea complex. The function of the trochlea is to redirect the tendon inferiorly, posteriorly, and laterally, with the tendon forming an angle of 51° with the visual axis or midplane of the eye in primary position (see Chapter 4, Fig 4-5). The tendon penetrates the Tenon capsule 2 mm nasally and 5 mm posteriorly to the nasal insertion of the superior rectus muscle. Passing under the superior rectus muscle, the tendon inserts posterior to the equator in the superotemporal quadrant of the eyeball, almost or entirely laterally to the midvertical plane or center of rotation.
The inferior oblique muscle originates from the periosteum of the maxillary bone, just posterior to the orbital rim and lateral to the orifice of the lacrimal fossa. It courses laterally, superiorly, and posteriorly, going inferior to the inferior rectus muscle and inserting under the lateral rectus muscle in the posterolateral portion of the globe, in the area of the macula. The inferior oblique muscle forms an angle of 51° with the visual axis or midplane of the eye in primary position (see Chapter 4, Fig 4-6). A stiff neurofibrovascular bundle containing the nerve to the inferior oblique runs anteriorly, along the lateral border of the inferior rectus muscle, to the myoneural junction. Most inferior oblique muscles have a single belly, but approximately 10% have 2 bellies; in rare cases, there are 3.
Table 3-1 Extraocular Muscles
Figure 3-2 The extrinsic muscles of the right eyeball in primary position, seen from above. Note that only the origin and insertion of the inferior oblique muscle are visible in this view.
(Modified with permission from Yanoff M, Duker J, eds. Ophthalmology. 2nd ed. London: Mosby; 2004:549.)
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.